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DTC P1600: Serial Communication Problem Between Pcm & TCM

  1. Turn ignition on. Measure voltage (backprobe) between ground and PCM 22-pin harness connector "C" terminal No. 5 (Green/White wire). If reading is 5 volts, go to step  3 . If reading is zero volts, go to next step. If reading toggles between zero and 5 volts, problem is intermittent or due to a faulty PCM or TCM. Go to INTERMITTENTS in TROUBLE SHOOTING - NO CODES article.
  2. Turn ignition off. Disconnect TCM harness connector. Turn ignition on. Measure voltage between ground and TCM terminal No. 17 (Green/White wire). If reading is 5 volts, check for an open in TCM power or ground circuits. Repair as necessary. If circuits are okay, replace TCM. If reading is not 5 volts, check Green/White wire between PCM and TCM for poor connection or short to ground. If wire is okay, replace PCM. Retest system.
  3. Check for poor connections or open Green/White wire between PCM and TCM. If okay, check for an open in TCM power or ground circuits. Repair as necessary. If wire and connections are okay, Replace TCM. Retest system.
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